1. Field of the Invention
This invention pertains to a method for forming nanocrystaline diamond films to be used for cold emission of electrons. More particularly, apparatus and method are disclosed for depositing such nanocrystalline diamond films on insulating or non-insulating substrates.
2. Description of the Related Art
Field emitters are used as electron sources in such applications as electron microscopes, flat panel displays and other vacuum microelectronics applications. In cathodoluminescence-based flat panel displays or field emission displays (FEDs), an array of field emitters acts as cold electron sources for the many pixels in the matrix display. The emission of each cold electron source is controlled by output voltages generated by solid state driver circuits. FED panels use color-emissive phosphors which are energized by emission from the array of field emitters. FED panels offer the potential for being energy-efficient, bright and providing saturated colors similar to those of a cathode ray tube (CRT). Such emitters have been reviewed in the article "Diamond-based field emission flat panel displays," Solid State Tech., May, 1995, p. 71. The characteristics needed for the cathode have been discussed in the article "Field Emission Characteristic Requirements for Field Emission Displays," 1994 Int'l. Display Res. Conf., Soc. for Info. Display, October 1994.
The use of a new glow discharge method for depositing diamond films was disclosed in the paper "Diamond film deposition by downstream d.c. glow discharge plasma chemical vapour deposition," Diamond and Related Materials, 1994. The emission properties of diamond films prepared by this method were not reported.
Although diamond thin film growth using the chemical vapor deposition (CVD) method has usually been assisted by only thermal or plasma energy, in the paper "Plasma-assisted CVD of diamond films by hollow cathode arc discharge," Diamond and Related Materials, 2, 1993, 413-416, the use of a combination of thermal and plasma decomposition of gas mixtures was suggested for a hollow cathode arc discharge. In a hollow cathode arc discharge, dissociation of the reactant gases occurs at the hot cathode surface and in the plasma between the electrodes. But, a hollow cathode arc discharge operates at a low pressure (up to 30 torr) only and has a limited deposition area up to only about 10 cm.sup.2. Also, hot cathode material may be sputtered by ions in a hollow cathode arc discharge and thereby may produce contamination of films. In a DC glow discharge, the cathode is cold and the hot anode is not bombarded by ions.
Although use of the diamond thin films described above has dramatically improved the emission qualities of field emitters, higher electron emission which is uniform over the diamond surface is needed. Methods and conditions for formation of CVD diamond thin films at an economical rate that will produce high emission currents that are more uniform over larger areas are needed.